The present invention relates to apparatus for accurate movement and positioning of a load, and in particular relates to a bi-fluid actuator for usage in accurately moving and positioning a load appropriately for use in automated movement, assembly manufacturing, related robotics tasks, and other industries requiring precise motion control.
Actuators are well known in automated assembly and related tasks that utilize pneumatic, mechanical or hydraulic positioning systems. For example, it is well known to utilize an actuator to move a load carriage in repetitive movements in assembly-line manufacturing. Typical actuators include rod actuators, wherein a piston within a hollow container variably moves a rod extending out of the container back and forth between desired positions, and a load or load carriage is secured to the rod. A rodless actuator includes a sliding piston within a hollow elongate container such as a cylinder, wherein the piston is secured mechanically or magnetically to a load carriage secured to a rail or support adjacent to the hollow object so that movement of the piston moves the load carriage.
Such actuators are often powered by hydraulic fluid utilizing a controller that pumps the fluid to a chamber on a first or an opposed second side of the piston, and that also permits movement of the hydraulic fluid out of the chamber into which the piston is to be moved. Such controllers also serve to detect the position of the piston, and stop movement when the piston and linked load carriage have achieved a desired position. Hydraulic actuators provide for precision of a rate of movement and positioning of the load, however they also have substantial drawbacks associated with a necessity of pumping a hydraulic fluid that is typically freeze and boiling resistant and hence is also often a hazardous waste, along with problems of the substantial cost, complexity and service requirements of pressurized hydraulic cylinders, seals, accumulators, by-pass valves, connecting lines to and from controllers, etc. Some actuators are electro-mechanically powered with electric motors, servo motors, threaded shafts, ball screws, toothed belts, etc. They also involve substantial cost in manufacture, substantial difficulties in accurate, rapid positioning of loads, and quite significant care and service requirements.
It is also known to power existing actuators with pneumatic, or compressible fluids such as air in order to minimize cost and the difficulties associated with hydraulic and electro-mechanical actuators. However, pneumatic actuators have substantial difficulties associated with characteristics of compressible fluids and chambers having variable dimensions, etc. For example, as a chamber on one side of a piston receives compressed air to move the piston away from that chamber, the piston resists movement due to stiction, wherein seals between the piston and an interior wall of the container housing the piston, such as a cylinder, tend to adhere to the cylinder wall as a function of a pressure of the incoming pressure of the compressed air. When the stiction resistance is finally overcome, the piston commences to move and it acquires an inertia of the load that tends to sustain movement of the piston at a lower force then that required to commence movement of the piston. As the piston moves within the cylinder, the dimensions of the chamber of the piston receiving the compressed air changes, so that a constant feed of the compressed air will not exert a constant force upon the piston, and compensation in the rate of delivery of the compressed air must be made if precision is required in a rate of movement of any load secured to the piston, or to a rod, or to a load carriage secured to the piston. A constant rate of movement of the piston will also be effected by variations in dynamic forces acting upon the load, such as mechanical linkages, etc., that will cause the load to change its resistance, thereby interrupting a constant rate of motion of the piston. When it is desired to stop the moving piston at a precise location, it is necessary to take into consideration a limited braking capacity of the compressible fluid within a chamber of the cylinder into which the piston is moving as the compressible fluid is compressed by the force of the moving piston. Because of the limited braking capacity of the compressible fluid, precise motion control is unobtainable under normal conditions.
Many efforts have been undertaken to provide pneumatic actuators that provide for a relatively constant rate of motion of a load carriage and that can accurately and rapidly position a load in a repetitive fashion between varying positions. One exemplary pneumatic linear actuator is sold under the trademark xe2x80x9cPRECISIONAIRExe2x80x9d by the TOL-O-MATIC, Inc. company of Hamel, Minn., U.S.A. The xe2x80x9cPRECISSIONAIRExe2x80x9d actuator utilizes an elongate, hollow container housing a piston linked to a load carriage, wherein the piston is also secured to a toothed belt that forms an endless loop extending between pulleys at opposed ends of the hollow container or cylinder. A complex proportional magnetic particle brake is secured to one pulley along with a rotary encoder that is in communication with a controller which cooperate to control a rate of motion of the load carriage by braking, and to control accurate positioning by the rotary encoder and controller. While such hybrid mechanical and pneumatic actuators offer some of the convenience of compressed air pneumatic actuators, they are nonetheless expensive to manufacture and service, and are essentially limited to linear actuators. In many situations, their accuracy for position location is not satisfactory for sensitive applications.
Accordingly, there is a need for an inexpensive actuator that provides the efficiency and low cost of pneumatic actuators with the precision of rates of motion and positioning provided by hydraulic actuators or servo motors for all applications from robotics to precision assembly.
The invention is a bi-fluid actuator for precise bi-directional movement and positioning of a mechanical object. The bi-fluid actuator includes a pneumatic fluid container containing a compressible, pneumatic fluid; a hydraulic fluid container containing a non-compressible, hydraulic fluid; a first mechanical object positioned between a first chamber and an opposed second chamber of the pneumatic fluid container so that the first mechanical object may be impacted and moved by the pneumatic fluid; a second mechanical object linked to the first mechanical object and positioned so that the second mechanical object may be impacted and positioned by the hydraulic fluid; a pneumatic fluid controller that selectively directs pressurized pneumatic fluid into either the first or opposed second chamber of the pneumatic fluid container; and a hydraulic fluid controller that selectively permits passage of the hydraulic fluid between the first and opposed second chambers of the hydraulic container, so that the pneumatic fluid controller selectively powers the first and linked second mechanical objects to move in either a first or opposed second direction, and the hydraulic fluid controller selectively permits movement and controls a rate of movement and position of the second and linked first mechanical object in the first or opposed second direction by selectively permitting, controlling a rate of, and then terminating passage of the hydraulic fluid between the opposed first and second chambers of the hydraulic fluid container. In essence, the hydraulic controller and hydraulic container form a closed loop hydraulic circuit that provides for flow control and accurate positioning while the pneumatic fluid powers movement of the first and second linked mechanical objects.
In an exemplary dual rod embodiment of the bi-fluid actuator, the pneumatic and hydraulic fluid containers are adjacent hollow, elongate containers, the first and second mechanical objects are pistons with rods within the hollow, elongate containers that are connected by way of the rods extending out of the containers to contact and move a load carriage typically utilized to precisely move an apparatus in automated assembly or manufacturing. By powering movement of the load carriage with a compressible or compressed, pneumatic fluid such as air, and controlling movement rate and positioning of the carriage with a non-compressible, fluid such as standard hydraulic fluid, precision of movement and positioning may be achieved by simply controlling passage of the non-compressible, hydraulic fluid at very modest pressure loads. The hydraulic fluid is selectively directed by the hydraulic fluid controller to flow through the controller between the first and second chambers of the hydraulic fluid container.
For example, if it is desired to move the load carriage away from the first chamber of the hydraulic fluid container, the chamber of the pneumatic fluid container aligned with the first chamber of the hydraulic fluid container receives compressed fluid from the pneumatic fluid controller. The hydraulic fluid controller then permits movement of the non-compressible, hydraulic fluid to pass from the second chamber into the first chamber of the hydraulic fluid container and the pneumatic fluid will then power movement of the linked first and second mechanical objects and load carriage away from the chamber having the compressed fluid, away from the first chamber of the hydraulic fluid container until a desired position of the load carriage is obtained. At that point the hydraulic fluid controller then terminates passage of the hydraulic fluid into the first chamber, thereby terminating further movement of the linked first and second mechanical objects and load carriage.
The bi-fluid actuator therefore provides for an elegant, low-powered, clean solution to precise movement of automated mechanical objects. Because the hydraulic fluid may control positioning at low pressure loads in a closed system, traditionally expensive and complicated sealing, feeding, and pressurizing of known hydraulic systems in automated actuators may be avoided. Because freely available, compressible, air fluid is utilized only for powering movement of the first mechanical object, and hence the load carriage, the known difficulties of accurate positioning of traditional pneumatic actuators is avoided. Accurate movement rates and positioning is achieved by movement of the second mechanical object by the hydraulic fluid through a cooperative integration of the hydraulic fluid controller with the pneumatic fluid controller. Additionally, because the powering source is readily available air, substantial power is available for moving high mass loads upon the load carriage without known cost and environmental risk factors associated with complex, highly pressurized hydraulic actuators.
Accordingly, it is a general object of the present invention to provide a bi-fluid actuator that overcomes deficiencies of prior actuators in accurate movement of a load.
It is a more specific object to provide a bi-fluid actuator that provides for precision of a rate of motion and of positioning of a load without pumping a non-compressible, hydraulic fluid.
It is yet another object to provide a bi-fluid actuator that may be utilized as a linear, or rotary actuator.
It is a further object to provide a bi-fluid actuator that may be produced utilizing either metal or plastic components.
It is still another object to provide a bi-fluid actuator that may be utilized as either a rodless actuator, or as a moving rod actuator.
These and other objects and advantages of this invention will become more readily apparent when the following description is read in conjunction with the accompanying drawings.